Spinning turbine blades for utility scale wind farms are considered by some to be a risk to birds that may pass through the surface swept by the turbine blades. Modern wind turbine and blade designs have reduced this risk greatly, primarily by designs that result in much slower blade rotation speeds. In the permitting process for wind farms, avian studies are undertaken to ascertain the potential for bird kills related to migrating birds, and changes made to turbine siting or other design issues to reduce the impact of the wind farm to passage birds.
However, government entities may require more active mitigation systems for certain protected bird or bat species. An example of this is the golden eagle, for which special mitigation methods may be required to be demonstrated before certain government entities will permit installation of the wind farm. Mitigation techniques under evaluation include the use of radar to locate birds entering the boundaries of a wind farm, and adjust the turbines based on the assumed flight path of such a bird.
However, while the ability to shut down specific wind turbines may reduce risk to birds, the aforementioned systems cannot generally classify a radar target as a specific species. These systems, for instance, cannot generally classify a golden eagle separately from a common turkey vulture or a large raven or other species that are not endangered or protected. This may result in a wind farm being shut down or curtailed far more often than the mitigation against a particular species of bird requires.
Government agencies allow the capture and light weight tagging of some species of wildlife to allow identification of that particular wildlife. An example of this might be the tagging of all golden eagles known to be nesting within 10 miles of the borders of a proposed wind farm. However, available tracking tags, such as GPS and VHF radio tags, are generally heavy, and will not remain active for the life of many birds (e.g., golden eagles often live up to 30 years in the wild). Solar powered tags have been introduced, but have been shown to have a high failure rate due to bird preening, debris on the solar cell, and other issues. Repeatedly capturing and tagging these birds may have detrimental consequences to the birds greater than the perceived risks of wind turbine blades that are being avoided by the use of tags. In addition, some animals such as golden eagles may be successfully captured and tagged once, but learn quickly to avoid similar capturing methods, and it may be very difficult to capture these animals multiple times.
In addition, GPS tags are designed to show the path of the bird only after the GPS has been recovered. Certain Argos (satellite system) GPS tags will return the location of the bird while still in flight, but only to a precision of about 250 to 1500 meters. GPS tags typically have a lengthy delay before data is received as to position, which would not be suitable for real time tracking of wildlife. VHF or GPS tags, which may be designed for battery life of up to 3 years, generally weigh a minimum of 30 grams. The weight and required mounting of these types of tags may have detrimental effects on a bird's life.
Opportunities exist for tracking birds and animals relative to dangerous situations such as wind turbines and roads to mitigate harm to such birds and animals.